1. Field of the Invention
This invention relates to magnetic metal particles, more particularly to a method for stabilizing magnetic metal particles.
2. Description of Related Art
Magnetic metal particles are usually used for manufacturing videotapes, audio tapes and disks which have high magnetization. One drawback is that the magnetic metal particles are easily oxidized, resulting in the easy reduction of the magnetization of the magnetic metal particles. Many methods for stabilizing magnetic metal particles have been disclosed in Japanese patents 64-21002 1989 , 63-299202 (1988), 52-155398 (1977), 52-21251 (1977) and 53-76958 (1978). In Japanese patent 64-21002 (1989), the stability of magnetic metal powder is improved by heat treatment. The resultant magnetic metal powder has a saturation magnetization of 130 emu/g and a magnetic coercive force of 1,500 Oe. After the resultant magnetic metal powder is subjected to a weather resistance test at 60.degree. C. and 90% RH for 7 days, the saturation magnetization thereof becomes 112 emu/g. In Japanese Patent 63-299202 (1988), the stability of magnetic metal powder is improved by applying a coating of aliphatic cyclic primary amine thereto. The resultant magnetic metal powder has a saturation magnetization of 124-125 emu/g. However, the improvement achieved by the prior inventions with respect to the saturation magnetization of the magnetic metal particles after the stabilization treatment is generally unsatisfactory.